1. Technical Field
The present invention relates to a semiconductor device containing a cylindrical capacitor, and a method of manufacturing the same.
2. Related Art
A memory cell of dynamic random access memory (DRAM) is composed of one transistor and one capacitor. Structure of the capacitor of DRAM has drastically changed with shrinkage of the semiconductor device. The capacitors for the memory cell is exemplified by those of flat type, stacked type, cylinder type, trench type and so forth, wherein the cylindrical capacitor is widely used at present as one of capacitor most suitable for higher integration.
The cylindrical capacitor is configured, as the name indicates, by stacking a lower electrode, an insulating film and an upper electrode in this order so as to cover a cylindrically patterned hole under good step coverage. Because the capacitor portion is formed after patterning the hole, the cylindrical capacitor is less likely to cause short-circuiting between the adjacent DRAM memory cells, and is therefore suitable for large scale integration. It has, however, been becoming more difficult for the capacitor, even if it were of cylindrical type, to ensure a sufficient level of capacitance under an increasing trend of downsizing, raising an expectation to a technique of increasing the capacitance anyhow.
Japanese Laid-Open Patent Publication No. H11-87650 describes a semiconductor device having a cylindrical capacitor. A method of manufacturing the semiconductor device having the cylindrical capacitor will be explained referring to FIGS. 5A to 6C.
First, a shown in FIG. 5A, a (second) insulating film 180 is formed over a silicon substrate 110, and a contact 190 is formed by a publicly-known method. An insulating interlayer 120 is then formed thereon (generally to as thick as 500 nm to 1.2 μm or around), and patterned through a photoresist film, to thereby form a hole 130. Then, as shown in FIG. 5B, an electroconductive lower electrode film 141 is formed.
Portion of the lower electrode film 141 fallen on the insulating interlayer 120 may be causative of short-circuiting between the adjacent DRAM memory cells, and must therefore be removed.
Possible methods of removing the lower electrode film 141 include those based on etchback and CMP (chemical mechanical polishing).
In the method based on etchback, the hole 130 is filled with a protective film 170 as shown in FIG. 5C, so as to prevent the lower electrode film 141 in the hole 130 from being etched. In general, a photoresist film is used as the protective film 170. In this configuration, the protective film 170 (photoresist film) may be left only inside the hole 130, if the film is appropriately exposed to light after formation thereof. The protective film 170 may readily be removed after the lower electrode film 141 was etched back. In this way, a part of the lower electrode film 141 is removed, and thereby a state shown in FIG. 5D may be obtained.
Next, as shown in FIG. 6A, a capacitor insulating film 142 and an electroconductive upper electrode 143 are successively formed. The capacitor insulating film 142 and the upper electrode 143 are then patterned using a photoresist film, to thereby obtain a structure shown in FIG. 6B. It is to be understood that, although the drawings herein show patterning for only a single DRAM memory cell for the convenience' sake, the capacitor insulating film 142 and the upper electrode 143 in practice are provided commonly with the other DRAM memory cells. Lastly, an insulating film 160 is formed so as to form a cylindrical capacitor 140 shown in FIG. 6C, to thereby obtain the semiconductor device.
Japanese Laid-Open Patent Publication No. H11-87650 describes a semiconductor integrated circuit device having a cylindrical capacitor. Japanese Laid-Open Patent Publication No. 2000-196039 describes a method of manufacturing a semiconductor memory device using CMP, aiming at preventing the lower electrode film or the like from being damaged by etching.
The present inventors have recognized as follows. Because the lower electrode film is removed by etchback in the procedures of the method of manufacturing a semiconductor device having a cylindrical capacitor as shown in FIGS. 5A to 5D and FIGS. 6A to 6C, the method has raised a problem in that the upper end portion of the lower electrode film 141 formed over the inner wall of the hole 130 may be removed by the etchback as shown in FIG. 5D. Such nonconformity has raised a problem in that the lower electrode film 141 may be reduced in the surface area, and thereby the capacitance may be reduced. Even if the protective film 170 (photoresist film) should be formed so as to completely fill the hole 130 as shown in FIG. 5C, it may be difficult to avoid loss or removal of the upper end portion of the lower electrode film 141 in the etchback.
On the other hand, the CMP process as described in Japanese Laid-Open Patent Publication No. 2000-196039 may be likely to generate dust or scratching, and may therefore be not suitable at present as a method of forming a capacitance susceptible to leakage through the capacitor film.